EP3152783A1 - Three dimensional nand device having a wavy charge storage layer - Google Patents

Three dimensional nand device having a wavy charge storage layer

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Publication number
EP3152783A1
EP3152783A1 EP15727191.7A EP15727191A EP3152783A1 EP 3152783 A1 EP3152783 A1 EP 3152783A1 EP 15727191 A EP15727191 A EP 15727191A EP 3152783 A1 EP3152783 A1 EP 3152783A1
Authority
EP
European Patent Office
Prior art keywords
charge storage
semiconductor channel
monolithic
opening
layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP15727191.7A
Other languages
German (de)
French (fr)
Inventor
Yanli Zhang
Matthias BAENNINGER
Akira MATSUDAIRA
Yao-Sheng Lee
Johann Alsmeier
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SanDisk Technologies LLC
Original Assignee
SanDisk Technologies LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by SanDisk Technologies LLC filed Critical SanDisk Technologies LLC
Publication of EP3152783A1 publication Critical patent/EP3152783A1/en
Pending legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
    • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
    • H01L29/10—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode not carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
    • H01L29/1025—Channel region of field-effect devices
    • H01L29/1029—Channel region of field-effect devices of field-effect transistors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B43/00—EEPROM devices comprising charge-trapping gate insulators
    • H10B43/20—EEPROM devices comprising charge-trapping gate insulators characterised by three-dimensional arrangements, e.g. with cells on different height levels
    • H10B43/23—EEPROM devices comprising charge-trapping gate insulators characterised by three-dimensional arrangements, e.g. with cells on different height levels with source and drain on different levels, e.g. with sloping channels
    • H10B43/27—EEPROM devices comprising charge-trapping gate insulators characterised by three-dimensional arrangements, e.g. with cells on different height levels with source and drain on different levels, e.g. with sloping channels the channels comprising vertical portions, e.g. U-shaped channels
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/78—Field effect transistors with field effect produced by an insulated gate
    • H01L29/792—Field effect transistors with field effect produced by an insulated gate with charge trapping gate insulator, e.g. MNOS-memory transistors
    • H01L29/7926—Vertical transistors, i.e. transistors having source and drain not in the same horizontal plane
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B43/00—EEPROM devices comprising charge-trapping gate insulators
    • H10B43/30—EEPROM devices comprising charge-trapping gate insulators characterised by the memory core region
    • H10B43/35—EEPROM devices comprising charge-trapping gate insulators characterised by the memory core region with cell select transistors, e.g. NAND

Definitions

  • the present invention relates generally to the field of semiconductor devices and specifically to three dimensional vertical NAND strings and other three dimensional devices and methods of making thereof.
  • S-SGT Structured Cell
  • IEDM Proc. (2001) 33-36 IEDM Proc.
  • this NAND string provides only one bit per cell.
  • the active regions of the NAND string is formed by a relatively difficult and time consuming process involving repeated formation of sidewall spacers and etching of a portion of the substrate, which results in a roughly conical active region shape.
  • a method of making a monolithic three dimensional NAND string comprises forming a stack of alternating first layers and second layers, wherein the first layers comprise an insulating material; etching the stack to form at least one opening in the stack to form a first curved profile in the first layers in the at least one opening and to form a second curved profile in the second layers in the at least one opening, wherein the second curved profile is different from the first curved profile; forming a charge storage layer in the at least one opening; forming a tunnel dielectric over the charge storage layer in the at least one opening; and forming a semiconductor channel over the tunnel dielectric in the at least one opening.
  • a monolithic, three dimensional NAND string comprises a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate; a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, the plurality of control gate electrodes comprising at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level; an interlevel insulating layer located between the first control gate electrode and the second control gate electrode; a blocking dielectric layer located in contact with the plurality of control gate electrodes and the interlevel insulating layer; a charge storage layer located at least partially in contact with the blocking dielectric layer, and comprising at least a first charge storage segment located in the first device level, a second charge storage segment located in the second device level, and a third charge storage segment located adjacent to the interlevel insulating layer between the first device level and the second device level
  • Another embodiment relates to a monolithic three dimensional NAND string including a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate and a plurality of control gate electrodes having a strip shape with major surfaces extending substantially parallel to the major surface of the substrate.
  • the plurality of control gate electrodes comprise at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level.
  • the string also includes a blocking dielectric layer located in contact with the plurality of control gate electrodes, a charge storage region comprising metal silicide nanoparticles embedded in a charge storage dielectric matrix, and a tunnel dielectric layer located between the charge storage region and the semiconductor channel.
  • Each monolithic three dimensional NAND string comprises a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of the substrate; a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprises at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level; an interlevel insulating layer located between the first control gate electrode and the second control gate electrode; a blocking dielectric layer located in contact with the plurality of control gate electrodes and the interlevel insulating layer; a charge storage layer located at least partially in contact with the blocking dielectric layer, and wherein the charge storage layer comprises at least a first charge storage segment
  • FIGS. 1 A- IB are respectively side cross sectional and top cross sectional views of a NAND string of one embodiment.
  • FIG. 1 A is a side cross sectional view of the device along line Y-Y' in FIG. IB
  • FIG. IB is a side cross sectional view of the device along line X-X' in FIG. 1A.
  • FIGS. 2A-2B are respectively side cross sectional and top cross sectional views of a NAND string of another embodiment.
  • FIG. 2A is a side cross sectional view of the device along line Y-Y' in FIG. 2B
  • FIG. 2B is a side cross sectional view of the device along line X-X' in FIG. 2A.
  • FIGS. 3-4 are side cross sectional views of NAND strings of another two embodiments.
  • FIGS. 5 A-5I illustrate a method of making a NAND string according to a first embodiment of the invention. DETAILED DESCRIPTION
  • the embodiments of the invention provide a monolithic, three dimensional array of memory devices, such as an array of vertical NAND strings.
  • the NAND strings are vertically oriented, such that at least one memory cell is located over another memory cell.
  • the array allows vertical scaling of NAND devices to provide a higher density of memory cells per unit area of silicon or other semiconductor material.
  • a monolithic three dimensional memory array is one in which multiple memory levels are formed above a single substrate, such as a semiconductor wafer, with no intervening substrates.
  • the term "monolithic" means that layers of each level of the array are directly deposited on the layers of each underlying level of the array.
  • two dimensional arrays may be formed separately and then packaged together to form a non- monolithic memory device.
  • non-monolithic stacked memories have been constructed by forming memory levels on separate substrates and adhering the memory levels atop each other, as in Leedy, U.S. Pat. No. 5,915,167, titled “Three Dimensional Structure Memory.” The substrates may be thinned or removed from the memory levels before bonding, but as the memory levels are initially formed over separate substrates, such memories are not true monolithic three dimensional memory arrays.
  • the monolithic three dimensional NAND string 150 comprises a semiconductor channel 1 having at least one end portion extending substantially perpendicular to a major surface 100a of a substrate 100, as shown in Figures 1 A and 2A.
  • the semiconductor channel 1 may have a pillar shape and the entire pillar- shaped semiconductor channel extends substantially perpendicularly to the major surface of the substrate 100, as shown in Figures 1 A and 2A.
  • the source/drain electrodes of the device can include a lower electrode 102a provided below the
  • the semiconductor channel 1 may have a U-shaped pipe shape, as shown in Figures 3 and 4.
  • the two wing portions la and lb of the U-shaped pipe shape semiconductor channel may extend substantially perpendicular to the major surface 100a of the substrate 100, and a connecting portion lc of the U-shaped pipe shape semiconductor channel 1 connects the two wing portions la, lb extends substantially parallel to the major surface 100a of the substrate 100.
  • one of the source or drain electrodes 102a contacts the first wing portion of the semiconductor channel from above, and another one of a source or drain electrodes 102b contacts the second wing portion of the semiconductor channel 1 from above.
  • An optional body contact electrode (not shown) may be disposed in the substrate 100 to provide body contact to the connecting portion of the semiconductor channel 1 from below.
  • the NAND string's select or access transistors are not shown in Figures 1 -4 for clarity.
  • the semiconductor channel 1 may have a J-shaped pipe shape (not shown).
  • a wing portion of the J-shaped pipe shape semiconductor channel may extend substantially perpendicular to the major surface of the substrate, and a second portion of the J-shaped pipe shape semiconductor channel extends substantially parallel to the major surface of the substrate.
  • one of the source or drain electrodes contacts the wing portion of the semiconductor channel from above, and another one of a source or drain electrodes contacts the second portion of the semiconductor channel from above or from below.
  • the semiconductor channel 1 may be a filled feature, as shown in Figures 2A-2B and 4.
  • the semiconductor channel 1 may be hollow, for example a hollow cylinder filled with an insulating fill material 2, as shown in Figures 1 A- IB and 3.
  • an insulating fill material 2 may be formed to fill the hollow part surrounded by the semiconductor channel 1.
  • the substrate 100 can be any semiconducting substrate known in the art, such as monocrystalline silicon, IV-IV compounds such as silicon-germanium or silicon-germanium- carbon, 1I1-V compounds, II-VI compounds, epitaxial layers over such substrates, or any other semiconducting or non-semiconducting material, such as silicon oxide, glass, plastic, metal or ceramic substrate.
  • the substrate 100 may include integrated circuits fabricated thereon, such as driver circuits for a memory device.
  • semiconductor channel 1 Any suitable semiconductor materials can be used for semiconductor channel 1 , for example silicon, germanium, silicon germanium, or other compound semiconductor materials, such as III-V, II-VI, or conductive or semiconductive oxides, etc. materials.
  • the semiconductor material may be amorphous, polycrystalline or single crystal.
  • semiconductor channel material may be formed by any suitable deposition methods.
  • the semiconductor channel material is deposited by low pressure chemical vapor deposition (LPCVD).
  • LPCVD low pressure chemical vapor deposition
  • semiconductor channel material may be a recrystallized polycrystalline semiconductor material formed by recrystallizing an initially deposited amorphous semiconductor material.
  • the insulating fill material 2 may comprise any electrically insulating material, such as silicon oxide, silicon nitride, silicon oxynitride, or other high-k insulating materials.
  • the monolithic three dimensional NAND string further comprise a plurality of control gate electrodes 3 alternating with a plurality of interlevel insulating layers 19, as shown in Figures 1 A- IB, 2A-2B, and 3-4.
  • the control gate electrodes 3 may comprise a portion having a strip shape extending substantially parallel to the major surface 100a of the substrate 100.
  • the plurality of control gate electrodes 3 comprise at least a first control gate electrode 3a located in a first device level (e.g., device level A) and a second control gate electrode 3b located in a second device level (e.g., device level B) located over the major surface 100a of the substrate 100 and below the device level A.
  • the control gate material may comprise any one or more suitable conductive or semiconductor control gate material known in the art, such as doped polysilicon, tungsten, copper, aluminum, tantalum, titanium, cobalt, titanium nitride or alloys thereof.
  • suitable conductive or semiconductor control gate material such as doped polysilicon, tungsten, copper, aluminum, tantalum, titanium, cobalt, titanium nitride or alloys thereof.
  • polysilicon is preferred to allow easy processing.
  • the monolithic three dimensional NAND string comprises a charge storage layer 9 located between a blocking dielectric 7 and the channel 1.
  • the charge storage layer 9 may be continuous, and may have a substantially uniform thickness.
  • the charge storage layer 9 having the substantially uniform thickness may have a variation in thickness in a horizontal direction parallel to the major surface 100a of less than or equal to 10%, such as from 0-10%, from 1-10%, or from 1-5% between device levels and interlevel regions adjacent to the interlevel insulating layers 19.
  • the charge storage layer 9 comprises at least a first charge storage segment 9a located in the device level A, a second charge storage segment 9b located in the device level B, and a third charge storage segment 9c located adjacent to the interlevel insulating layer 19b between the device level A and the device level B, as shown in Figures 1 A, 2A, 3 and 4.
  • the charge storage layer has a curved profile along at least one of the first charge storage segment 9a and the third charge storage segment 9c.
  • the charge storage layer 9 has a first curved profile along a first charge storage segment 9a, and a different, second curved profile along the third charge storage segment 9c.
  • the second charge storage segment 9b may have the same curved profile as the first charge storage segment 9a.
  • the first charge storage segment 9a is convex in the direction of the first control gate electrode 3 a
  • the third charge storage segment 9c is concave in the direction of the interlevel insulating layer 19b, as shown in Figures 3 and 4.
  • the blocking dielectric 7 is located adjacent to the control gate(s) 3 and may surround the control gate 3 (not shown).
  • the blocking dielectric 7 may be continuous, and may have a substantially uniform thickness.
  • dielectric 7 having the substantially uniform thickness may have a variation in thickness in a horizontal direction parallel to the major surface 100a of less than or equal to 10%, such as from 0-10%, from 1-10%, or from 1- 5% between device levels and interlevel regions adjacent to the interlevel insulating layers 19.
  • the blocking dielectric 7 comprises a plurality of blocking dielectric segments located in contact with a respective one of the plurality of control gate electrodes 3, for example a first dielectric segment 7a located in device level A and a second dielectric segment 7b located in device level B are in contact with control electrodes 3a and 3b, respectively, as shown in Figures 3 and 4.
  • the blocking dielectric 7 may have a complementary curved profile to the charge storage layer 9 along at least one segment where the blocking dielectric 7 is in contact with the charge storage layer 9. In other words, if a particular segment of the charge storage layer 9 is convex, then the adjacent segment of the blocking dielectric 7 is also convex, and vice versa.
  • the tunnel dielectric 1 1 of the monolithic three dimensional NAND string is located between the charge storage layer 9 and the semiconductor channel 1.
  • the tunnel dielectric 1 1 may be continuous, and may have a substantially uniform thickness.
  • the tunnel dielectric 11 having the substantially uniform thickness may have a variation in thickness in a horizontal direction parallel to the major surface 100a of less than or equal to 10%, such as from 0-10%, from 1-10%, or from 1-5% between device levels and interlevel regions adjacent to the interlevel insulating layers 19.
  • the tunnel dielectric 1 1 may have a complementary curved profile to the charge storage layer 9 along at least one segment where the tunnel dielectric 1 1 is in contact with the charge storage layer 9. In other words, if a particular segment of the charge storage layer 9 is convex, then the adjacent segment of the tunnel dielectric 1 1 is also convex, and vice versa.
  • the blocking dielectric 7 and the tunnel dielectric 1 1 may be independently selected from any one or more same or different electrically insulating materials, such as silicon oxide, silicon nitride, silicon oxynitride, metal oxide (e.g., AI2O3 or Hf0 2 ), or other high-k insulating materials.
  • the blocking dielectric 7 and/or the tunnel dielectric 1 1 may include multiple layers of silicon oxide, silicon nitride and/or silicon oxynitride (e.g., ONO layers) for tunnel dielectric 1 1, or silicon oxide and metal oxide for blocking dielectric 7.
  • the charge storage layer 9 may comprise a conductive (e.g., metal or metal alloy such as titanium, platinum, ruthenium, titanium nitride, hafnium nitride, tantalum nitride, zirconium nitride, or a metal silicide such as titanium silicide, nickel silicide, cobalt silicide, or a combination thereof) or semiconductor (e.g., polysilicon) floating gate, conductive nanoparticles, or a charge storage dielectric (e.g., silicon nitride or another dielectric) feature.
  • the charge storage layer 9 is a continuous charge storage dielectric which extends continuously along the channel 1 substantially perpendicular to the major surface 100a.
  • the charge storage layer 9 comprises discrete floating gates described above or discrete charge storage dielectric features, each of which comprises a nitride feature adjacent the respective blocking dielectric 7, where the silicon oxide blocking dielectric 7, the nitride feature 9 and the silicon oxide tunnel dielectric 1 1 form oxide-nitride-oxide discrete charge storage structures of the NAND string.
  • the semiconductor channel 1 has a complementary curved profile to the tunnel dielectric 1 1 along at least one segment where the semiconductor channel 1 is in contact with the tunnel dielectric 1 1. In other words, if a particular segment of the tunnel dielectric 1 1 and an adjacent segment of the charge storage layer 9 are convex, then the adjacent segment of the semiconductor channel 1 is also convex, and vice versa.
  • a segment of the NAND string perpendicular to the major surface 100a of the substrate 100 has a wavy profile, as shown in Figures 1 A, 2 A, 3, and 4.
  • a wavy profile is defined as having one or more layers with complementary plural alternating convex/concave segments, where each segment has a non-zero radius of curvature.
  • the amplitude of the waviness is not less than 15% of the vertical separation between two neighboring gates.
  • the blocking dielectric 7, the charge storage layer 9, and the tunnel dielectric 1 1 may each have a substantially uniform thickness. If the semiconductor channel 1 is a filled feature, as shown in Figures 2A-2B and 4, the
  • semiconductor channel 1 of Figures 2A-2B, or the two wing portions 1 a and 1 b of the semiconductor channel 1 of Figure 4 are quasi-cylindrical bodies having a variable thickness in a direction perpendicular to the major surface 100a of the substrate 100.
  • the semiconductor channel 1 of Figures 1 A- IB or the two wing portions la and lb of the semiconductor channel of Figure 3 have a wavy profile with a substantially uniform thickness
  • the insulating fill material 2 is a quasi- cylindrical body having a variable thickness in a direction perpendicular to the major surface 100a of the substrate 100.
  • the wavy profile of the charge storage layer 9 results in a longer profile (in a direction substantially perpendicular to the major surface 100a) of the first and second curved charge storage segments 9a, 9b along the control gates 3a, 3b than a comparable flat segment of the charge storage layer.
  • This longer, curved charge storage segments 9a, 9b provide a longer diffusion path for trapped electrons, and therefore reduces leakage to adjacent cells.
  • the wavy profile of the charge storage layer 9 also enhances the electric field for the programmed cell (along charge storage segments 9a, 9b), and reduces the electric field in the spacing region adjacent the interlevel insulating layers (along charge storage segment 9c). As a result, interference between cells is reduced.
  • Figures 5A-5I illustrate a method of making a NAND string according to a first embodiment of the invention.
  • an optional etch stop layer 202a is formed over the major surface 100a of the substrate 100.
  • the etch stop layer 202a may be, for example, a polysilicon layer.
  • the etch stop layer 202a comprises a conductive or heavily doped semiconductor (e.g., n or p-type doped with a concentration of at least 10 18 cm 3 ) material, and the etch stop layer 202a forms the electrode 102a.
  • the etch stop layer 202a comprises a sacrificial material, at least a portion of which is removed to provide a space to form an electrode 102a.
  • the etch stop layer 202a is an insulating or semiconductor material and remains in the completed device 150. In yet other embodiments, etch stop layer 202a is omitted.
  • a stack 120 of alternating first layers 19 (19a, 19b, etc.) and second layers 122 (122a, 122b, etc.) are formed over the etch stop layer 202a or over the major surface 100a of substrate 100 if the etch stop layer 202a is omitted.
  • First layers 19 and second layers 122 may be deposited over the substrate by any suitable deposition method, such as sputtering, CVD, MBE, etc.
  • First layers 19 may comprise an insulating material, for example a silicon oxide, in one embodiment, second layers 122 may comprise a conductive or semiconductive material, and the second layers 122 form the plurality of control gate electrodes 3.
  • second layers 122 are sacrificial layers, and may comprise a sacrificial material, such as intrinsic polysilicon or an insulating material (e.g., silicon nitride, silicon oxide, etc.).
  • the second layers 122 are removed, and a plurality of control gate electrodes is formed in their place by a replacement process.
  • first layers 19 and second layers 122 are followed by etching the stack 120 to form at least one opening 84 in the stack 120, as shown in Figure 5c.
  • An array of openings 84 may be formed in locations where vertical channels or channel portions of NAND strings will be subsequently formed.
  • the etching process forms a first curved profile 84c in the first layers 19, and a second curved profile 84a, 84b in the second layers 122. As shown in Figure 5C, the first curved profile 84c is different from the second curved profile 84a, 84b.
  • the first curved profile 84c is convex in the direction of the opening 84 (i.e., curved sides of first layers 19 protrude into the opening 84), and the second curved profile 84a, 84b is concave in the direction of the opening 84 (i.e., curved sides of second layers 122 in the opening 84 curve inward into second layers 122).
  • the etching of the stack comprises a dry etching process which results in the first curved profile 84c and the second curved profile 84a, 84b.
  • the dry etching process may be performed at any combination of parameters (e.g., pressure, temperature, chemical etchant, etc.) that results in the curved profile of the opening 84.
  • the etching of the stack comprises a first anisotropic etching process followed by a second selective etching process.
  • the first dry etching process may be a reactive ion etch
  • the second selective etching process is a selective isotropic wet or dry etch which selectively recesses the second layers 122 compared to the first layers 19 to form the first curved profile 84c and the second curved profile 84a, 84b.
  • the etching of the stack is performed in a single step.
  • a blocking dielectric 7 (also known as an inter-poly dielectric, IPD) is then formed in the opening 84 such that the blocking dielectric coats the sides of the opening 84, resulting in a structure as shown in Figure 5D.
  • the blocking dielectric 7 may comprise a silicon oxide layer deposited by conformal atomic layer deposition (ALD) or chemical vapor deposition (CVD).
  • ALD conformal atomic layer deposition
  • CVD chemical vapor deposition
  • Other high-k dielectric materials such as hafnium oxide or aluminum oxide, or multi-layer dielectrics (e.g., ONO) may be used instead or in addition to silicon oxide.
  • an insulating capping layer (e.g., silicon nitride) may be deposited into the openings before the blocking dielectric 7 and may comprise a back portion of a multi-layer blocking dielectric.
  • the blocking dielectric 7 follows the curvature of the opening 84 to form a first curved blocking segment 7c on the first layers 19, and second curved blocking segments 7a, 7b on the second layers 122.
  • the blocking dielectric 7 has a substantially uniform thickness, and the first curved blocking segment 7c is convex in the direction of the opening 84, and the second curved blocking segments 7a, 7b are concave in the direction of the opening 84.
  • a charge storage layer 9 is formed in the openings 84 over the blocking dielectric material 7, resulting in the structure shown in Figure 5E.
  • the charge storage layer 9 may comprise a charge storage dielectric material (e.g., silicon nitride).
  • the charge storage layer 9 may comprise a conductive or semiconductor floating gate material (e.g., a metal, metal alloy such as TiN, metal silicide, or heavily doped polysilicon floating gate material). Any desired methods may be used to form the charge storage layer 9, such as ALD or CVD.
  • the charge storage layer 9 follows the curvature of the blocking dielectric 7 to form a first curved charge storage segment 9c over the first layers 19, and second curved charge storage segments 9a, 9b over the second layers 122.
  • the charge storage layer 9 has a substantially uniform thickness, and the first curved charge storage segment 9c is convex in the direction of the opening 84, and the second curved charge storage segments 9a, 9b are concave in the direction of the opening 84.
  • the first charge storage segment 9c is concave in the direction of the first layers 19, and the second charge storage segments 9a, 9b are convex in the direction of the second layers 122.
  • the tunnel dielectric 1 1 is deposited in the opening 84, over the charge storage layer 9, as shown in Figure 5F. This may be accomplished, for example by depositing the tunnel dielectric material 1 1 with a chemical vapor deposition (CVD) processor an atomic layer deposition (ALD) process.
  • CVD chemical vapor deposition
  • ALD atomic layer deposition
  • the tunnel dielectric 1 1 follows the curvature of the charge storage layer 9 to form a first curved tunnel segment 1 lc over the first layers 19, and second curved tunnel segments 1 1a, l ib over the second layers 122.
  • the tunnel dielectric 1 1 has a substantially uniform thickness, and the first curved tunnel segment 1 lc is convex in the direction of the opening 84, and the second curved tunnel segments 11a, 1 lb are concave in the direction of the opening 84.
  • the charge storage layer 9 and the tunnel dielectric 1 1 have a wavy profile along substantially the length of the opening 84.
  • the channel 1 may be formed by depositing the semiconductor channel 1 , which comprises a semiconductor material, such as a lightly doped or intrinsic polysilicon, in the opening 84. As discussed above, the entire opening 84 may be filled to form the device illustrated in Figures 2A, 2B, and 4. In various embodiments, the semiconductor channel 1 has a circular cross section when viewed from above, and the semiconductor channel 1 completely fills the opening 84 with a semiconductor channel material. Alternatively, the semiconductor channel 1 may first be deposited in the opening 84 followed by deposition of an insulating fill 2 to form the device illustrated in Figures 1 A, I B, and 3.
  • the semiconductor channel 1 may first be deposited in the opening 84 followed by deposition of an insulating fill 2 to form the device illustrated in Figures 1 A, I B, and 3.
  • the semiconductor channel 1 has a circular cross section when viewed from above, and the semiconductor channel material is formed over the side wall of the opening 84 but not in a central part of the opening 84 such that the semiconductor channel material does not completely fill the opening 84.
  • An insulating fill 2 is formed in the central part of the opening 84 to completely fill the opening 84.
  • the channel 1 may be U-shaped, as illustrated in Figures 3 and 4.
  • the semiconductor channel 1 follows the curvature of the tunnel dielectric 1 1 to form a first curved channel segment lc over the first layers 19, and second curved channel segments la, lb over the second layers 122.
  • the semiconductor channel 1 has a substantially uniform thickness, and the first curved channel segment lc is convex in the direction of the opening 84, and the second curved channel segments la, lb are concave in the direction of the opening 84.
  • the insulating fill 2 is deposited to fill the opening in the semiconductor channel 1.
  • the insulating fill 2 follows the curvature of the semiconductor channel 1 to form a quasi -cylindrical body having a variable thickness in a direction perpendicular to the major surface 100a of the substrate 100.
  • Figure 51 shows the completed NAND string 150 including the plurality of control gate electrodes 3 and source and drain electrodes 102a, 102b formed in electrical contact with respective end portions of the semiconductor channel 1.
  • a first electrode 102b is formed in electrical contact with an upper end of the semiconductor channel 1
  • a second electrode 102a is formed in electrical contact with a lower end of the semiconductor channel 1.
  • the plurality of control gate electrodes 3 are formed by etching the stack 120 to form a backside opening 184 (e.g., a slit trench or source electrode opening) in the stack such that the etch stop layer 202a is exposed.
  • the etch stop layer 202a and the second layers 122 are removed from the stack 120 through backside opening 184 to form a plurality of recesses between the first layers 19, and the plurality of electrically conductive (e.g., metal, such as tungsten and/or metal nitride, such as TiN) control gates 3 and the source electrode 102a are formed in the plurality of recesses through the backside opening 184.
  • each of the plurality of control gates 3 has a profile complementary to the charge storage layer 9.
  • the source electrode 102a is in electrical contact with the lower end of the semiconductor channel 1 in the backside opening 184
  • the drain electrode 102b is in electrical contact with the upper end of the semiconductor channel 1.

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Abstract

A monolithic three dimensional NAND string includes a semiconductor channel, where at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate, a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, an interlevel insulating layer located between adjacent control gate electrodes, a blocking dielectric layer located in contact with the plurality of control gate electrodes and an interlevel insulating layer, a charge storage layer located at least partially in contact with the blocking dielectric layer, and a tunnel dielectric located between the charge storage layer and the semiconductor channel. The charge storage layer has a curved profile.

Description

THREE DIMENSIONAL NAND DEVICE HAVING A WAVY CHARGE STORAGE
LAYER
RELATED APPLICATIONS
[0001] The present application is related to and claims priority to U.S. Application No. 14/297,106, filed June 5, 2014, the entire contents of which are incorporated by reference herein.
FIELD
[0002] The present invention relates generally to the field of semiconductor devices and specifically to three dimensional vertical NAND strings and other three dimensional devices and methods of making thereof.
BACKGROUND
[0003] Three dimensional vertical NAND strings are disclosed in an article by T. Endoh, et. al., titled "Novel Ultra High Density Memory With A Stacked-Surrounding Gate
Transistor (S-SGT) Structured Cell", IEDM Proc. (2001) 33-36. However, this NAND string provides only one bit per cell. Furthermore, the active regions of the NAND string is formed by a relatively difficult and time consuming process involving repeated formation of sidewall spacers and etching of a portion of the substrate, which results in a roughly conical active region shape.
SUMMARY
[0004] According to one embodiment of the invention, a method of making a monolithic three dimensional NAND string comprises forming a stack of alternating first layers and second layers, wherein the first layers comprise an insulating material; etching the stack to form at least one opening in the stack to form a first curved profile in the first layers in the at least one opening and to form a second curved profile in the second layers in the at least one opening, wherein the second curved profile is different from the first curved profile; forming a charge storage layer in the at least one opening; forming a tunnel dielectric over the charge storage layer in the at least one opening; and forming a semiconductor channel over the tunnel dielectric in the at least one opening.
[0005] According to another embodiment of the invention, a monolithic, three dimensional NAND string comprises a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate; a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, the plurality of control gate electrodes comprising at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level; an interlevel insulating layer located between the first control gate electrode and the second control gate electrode; a blocking dielectric layer located in contact with the plurality of control gate electrodes and the interlevel insulating layer; a charge storage layer located at least partially in contact with the blocking dielectric layer, and comprising at least a first charge storage segment located in the first device level, a second charge storage segment located in the second device level, and a third charge storage segment located adjacent to the interlevel insulating layer between the first device level and the second device level; and a tunnel dielectric located between the charge storage layer and the semiconductor channel. The charge storage layer has a curved profile along at least one of the first charge storage segment and the third charge storage segment.
[0006] Another embodiment relates to a monolithic three dimensional NAND string including a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate and a plurality of control gate electrodes having a strip shape with major surfaces extending substantially parallel to the major surface of the substrate. The plurality of control gate electrodes comprise at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level. The string also includes a blocking dielectric layer located in contact with the plurality of control gate electrodes, a charge storage region comprising metal silicide nanoparticles embedded in a charge storage dielectric matrix, and a tunnel dielectric layer located between the charge storage region and the semiconductor channel.
[0007] According to another embodiment of the invention, a monolithic three
dimensional NAND memory device, comprises a silicon substrate; an array of monolithic three dimensional NAND strings having a plurality of device levels disposed above the silicon substrate; and driver circuits associated with the array located above or in the silicon substrate. Each monolithic three dimensional NAND string comprises a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of the substrate; a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprises at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level; an interlevel insulating layer located between the first control gate electrode and the second control gate electrode; a blocking dielectric layer located in contact with the plurality of control gate electrodes and the interlevel insulating layer; a charge storage layer located at least partially in contact with the blocking dielectric layer, and wherein the charge storage layer comprises at least a first charge storage segment located in the first device level, a second charge storage segment located in the second device level, and a third charge storage segment located adjacent to the interlevel insulating layer between the first device level and the second device level; and a tunnel dielectric located between the charge storage layer and the semiconductor channel. The charge storage layer has a curved profile along at least one of the first charge storage segment and the third charge storage segment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1 A- IB are respectively side cross sectional and top cross sectional views of a NAND string of one embodiment. FIG. 1 A is a side cross sectional view of the device along line Y-Y' in FIG. IB, while FIG. IB is a side cross sectional view of the device along line X-X' in FIG. 1A.
[0009] FIGS. 2A-2B are respectively side cross sectional and top cross sectional views of a NAND string of another embodiment. FIG. 2A is a side cross sectional view of the device along line Y-Y' in FIG. 2B, while FIG. 2B is a side cross sectional view of the device along line X-X' in FIG. 2A.
[0010] FIGS. 3-4 are side cross sectional views of NAND strings of another two embodiments.
[0011] FIGS. 5 A-5I illustrate a method of making a NAND string according to a first embodiment of the invention. DETAILED DESCRIPTION
[0012] Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the following description is intended to describe exemplary embodiments of the invention, and not to limit the invention.
[0013] The embodiments of the invention provide a monolithic, three dimensional array of memory devices, such as an array of vertical NAND strings. The NAND strings are vertically oriented, such that at least one memory cell is located over another memory cell. The array allows vertical scaling of NAND devices to provide a higher density of memory cells per unit area of silicon or other semiconductor material.
[0014] A monolithic three dimensional memory array is one in which multiple memory levels are formed above a single substrate, such as a semiconductor wafer, with no intervening substrates. The term "monolithic" means that layers of each level of the array are directly deposited on the layers of each underlying level of the array. In contrast, two dimensional arrays may be formed separately and then packaged together to form a non- monolithic memory device. For example, non-monolithic stacked memories have been constructed by forming memory levels on separate substrates and adhering the memory levels atop each other, as in Leedy, U.S. Pat. No. 5,915,167, titled "Three Dimensional Structure Memory." The substrates may be thinned or removed from the memory levels before bonding, but as the memory levels are initially formed over separate substrates, such memories are not true monolithic three dimensional memory arrays.
[0015] In some embodiments, the monolithic three dimensional NAND string 150 comprises a semiconductor channel 1 having at least one end portion extending substantially perpendicular to a major surface 100a of a substrate 100, as shown in Figures 1 A and 2A. For example, the semiconductor channel 1 may have a pillar shape and the entire pillar- shaped semiconductor channel extends substantially perpendicularly to the major surface of the substrate 100, as shown in Figures 1 A and 2A. In these embodiments, the source/drain electrodes of the device can include a lower electrode 102a provided below the
semiconductor channel 1 and an upper electrode 102b formed over the semiconductor channel 1, as shown in Figures 1 A and 2 A.
[0016] Alternatively, the semiconductor channel 1 may have a U-shaped pipe shape, as shown in Figures 3 and 4. The two wing portions la and lb of the U-shaped pipe shape semiconductor channel may extend substantially perpendicular to the major surface 100a of the substrate 100, and a connecting portion lc of the U-shaped pipe shape semiconductor channel 1 connects the two wing portions la, lb extends substantially parallel to the major surface 100a of the substrate 100. In these embodiments, one of the source or drain electrodes 102a contacts the first wing portion of the semiconductor channel from above, and another one of a source or drain electrodes 102b contacts the second wing portion of the semiconductor channel 1 from above. An optional body contact electrode (not shown) may be disposed in the substrate 100 to provide body contact to the connecting portion of the semiconductor channel 1 from below. The NAND string's select or access transistors are not shown in Figures 1 -4 for clarity.
[0017] In an alternative embodiment, the semiconductor channel 1 may have a J-shaped pipe shape (not shown). A wing portion of the J-shaped pipe shape semiconductor channel may extend substantially perpendicular to the major surface of the substrate, and a second portion of the J-shaped pipe shape semiconductor channel extends substantially parallel to the major surface of the substrate. In these embodiments, one of the source or drain electrodes contacts the wing portion of the semiconductor channel from above, and another one of a source or drain electrodes contacts the second portion of the semiconductor channel from above or from below.
{0018] In some embodiments, the semiconductor channel 1 may be a filled feature, as shown in Figures 2A-2B and 4. In some other embodiments, the semiconductor channel 1 may be hollow, for example a hollow cylinder filled with an insulating fill material 2, as shown in Figures 1 A- IB and 3. In these embodiments, and an insulating fill material 2 may be formed to fill the hollow part surrounded by the semiconductor channel 1.
[0019] The substrate 100 can be any semiconducting substrate known in the art, such as monocrystalline silicon, IV-IV compounds such as silicon-germanium or silicon-germanium- carbon, 1I1-V compounds, II-VI compounds, epitaxial layers over such substrates, or any other semiconducting or non-semiconducting material, such as silicon oxide, glass, plastic, metal or ceramic substrate. The substrate 100 may include integrated circuits fabricated thereon, such as driver circuits for a memory device.
[0020] Any suitable semiconductor materials can be used for semiconductor channel 1 , for example silicon, germanium, silicon germanium, or other compound semiconductor materials, such as III-V, II-VI, or conductive or semiconductive oxides, etc. materials. The semiconductor material may be amorphous, polycrystalline or single crystal. The
semiconductor channel material may be formed by any suitable deposition methods. For example, in one embodiment, the semiconductor channel material is deposited by low pressure chemical vapor deposition (LPCVD). In some other embodiments, the
semiconductor channel material may be a recrystallized polycrystalline semiconductor material formed by recrystallizing an initially deposited amorphous semiconductor material.
[0021] The insulating fill material 2 may comprise any electrically insulating material, such as silicon oxide, silicon nitride, silicon oxynitride, or other high-k insulating materials.
[0022] The monolithic three dimensional NAND string further comprise a plurality of control gate electrodes 3 alternating with a plurality of interlevel insulating layers 19, as shown in Figures 1 A- IB, 2A-2B, and 3-4. The control gate electrodes 3 may comprise a portion having a strip shape extending substantially parallel to the major surface 100a of the substrate 100. The plurality of control gate electrodes 3 comprise at least a first control gate electrode 3a located in a first device level (e.g., device level A) and a second control gate electrode 3b located in a second device level (e.g., device level B) located over the major surface 100a of the substrate 100 and below the device level A. The control gate material may comprise any one or more suitable conductive or semiconductor control gate material known in the art, such as doped polysilicon, tungsten, copper, aluminum, tantalum, titanium, cobalt, titanium nitride or alloys thereof. For example, in some embodiments, polysilicon is preferred to allow easy processing.
[0023] The monolithic three dimensional NAND string comprises a charge storage layer 9 located between a blocking dielectric 7 and the channel 1. The charge storage layer 9 may be continuous, and may have a substantially uniform thickness. For example the charge storage layer 9 having the substantially uniform thickness may have a variation in thickness in a horizontal direction parallel to the major surface 100a of less than or equal to 10%, such as from 0-10%, from 1-10%, or from 1-5% between device levels and interlevel regions adjacent to the interlevel insulating layers 19. The charge storage layer 9 comprises at least a first charge storage segment 9a located in the device level A, a second charge storage segment 9b located in the device level B, and a third charge storage segment 9c located adjacent to the interlevel insulating layer 19b between the device level A and the device level B, as shown in Figures 1 A, 2A, 3 and 4. [0024] The charge storage layer has a curved profile along at least one of the first charge storage segment 9a and the third charge storage segment 9c. In some embodiments, the charge storage layer 9 has a first curved profile along a first charge storage segment 9a, and a different, second curved profile along the third charge storage segment 9c. The second charge storage segment 9b may have the same curved profile as the first charge storage segment 9a. In an embodiment, the first charge storage segment 9a is convex in the direction of the first control gate electrode 3 a, and the third charge storage segment 9c is concave in the direction of the interlevel insulating layer 19b, as shown in Figures 3 and 4.
[0025] The blocking dielectric 7 is located adjacent to the control gate(s) 3 and may surround the control gate 3 (not shown). The blocking dielectric 7 may be continuous, and may have a substantially uniform thickness. For example, dielectric 7 having the substantially uniform thickness may have a variation in thickness in a horizontal direction parallel to the major surface 100a of less than or equal to 10%, such as from 0-10%, from 1-10%, or from 1- 5% between device levels and interlevel regions adjacent to the interlevel insulating layers 19. The blocking dielectric 7 comprises a plurality of blocking dielectric segments located in contact with a respective one of the plurality of control gate electrodes 3, for example a first dielectric segment 7a located in device level A and a second dielectric segment 7b located in device level B are in contact with control electrodes 3a and 3b, respectively, as shown in Figures 3 and 4.
[0026] The blocking dielectric 7 may have a complementary curved profile to the charge storage layer 9 along at least one segment where the blocking dielectric 7 is in contact with the charge storage layer 9. In other words, if a particular segment of the charge storage layer 9 is convex, then the adjacent segment of the blocking dielectric 7 is also convex, and vice versa. [0027] The tunnel dielectric 1 1 of the monolithic three dimensional NAND string is located between the charge storage layer 9 and the semiconductor channel 1. The tunnel dielectric 1 1 may be continuous, and may have a substantially uniform thickness. For example, the tunnel dielectric 11 having the substantially uniform thickness may have a variation in thickness in a horizontal direction parallel to the major surface 100a of less than or equal to 10%, such as from 0-10%, from 1-10%, or from 1-5% between device levels and interlevel regions adjacent to the interlevel insulating layers 19. The tunnel dielectric 1 1 may have a complementary curved profile to the charge storage layer 9 along at least one segment where the tunnel dielectric 1 1 is in contact with the charge storage layer 9. In other words, if a particular segment of the charge storage layer 9 is convex, then the adjacent segment of the tunnel dielectric 1 1 is also convex, and vice versa.
[0028] The blocking dielectric 7 and the tunnel dielectric 1 1 may be independently selected from any one or more same or different electrically insulating materials, such as silicon oxide, silicon nitride, silicon oxynitride, metal oxide (e.g., AI2O3 or Hf02), or other high-k insulating materials. The blocking dielectric 7 and/or the tunnel dielectric 1 1 may include multiple layers of silicon oxide, silicon nitride and/or silicon oxynitride (e.g., ONO layers) for tunnel dielectric 1 1, or silicon oxide and metal oxide for blocking dielectric 7.
[0029] The charge storage layer 9 may comprise a conductive (e.g., metal or metal alloy such as titanium, platinum, ruthenium, titanium nitride, hafnium nitride, tantalum nitride, zirconium nitride, or a metal silicide such as titanium silicide, nickel silicide, cobalt silicide, or a combination thereof) or semiconductor (e.g., polysilicon) floating gate, conductive nanoparticles, or a charge storage dielectric (e.g., silicon nitride or another dielectric) feature. Preferably, the charge storage layer 9 is a continuous charge storage dielectric which extends continuously along the channel 1 substantially perpendicular to the major surface 100a. In some embodiments, the charge storage layer 9 comprises discrete floating gates described above or discrete charge storage dielectric features, each of which comprises a nitride feature adjacent the respective blocking dielectric 7, where the silicon oxide blocking dielectric 7, the nitride feature 9 and the silicon oxide tunnel dielectric 1 1 form oxide-nitride-oxide discrete charge storage structures of the NAND string.
[0030] In some embodiments, the semiconductor channel 1 has a complementary curved profile to the tunnel dielectric 1 1 along at least one segment where the semiconductor channel 1 is in contact with the tunnel dielectric 1 1. In other words, if a particular segment of the tunnel dielectric 1 1 and an adjacent segment of the charge storage layer 9 are convex, then the adjacent segment of the semiconductor channel 1 is also convex, and vice versa.
[0031] In various embodiments, a segment of the NAND string perpendicular to the major surface 100a of the substrate 100 has a wavy profile, as shown in Figures 1 A, 2 A, 3, and 4. A wavy profile is defined as having one or more layers with complementary plural alternating convex/concave segments, where each segment has a non-zero radius of curvature. Preferably, the amplitude of the waviness is not less than 15% of the vertical separation between two neighboring gates. The blocking dielectric 7, the charge storage layer 9, and the tunnel dielectric 1 1 may each have a substantially uniform thickness. If the semiconductor channel 1 is a filled feature, as shown in Figures 2A-2B and 4, the
semiconductor channel 1 of Figures 2A-2B, or the two wing portions 1 a and 1 b of the semiconductor channel 1 of Figure 4 are quasi-cylindrical bodies having a variable thickness in a direction perpendicular to the major surface 100a of the substrate 100. In some other embodiments, shown in Figures 1 A- IB and 3, where the semiconductor channel 1 is hollow and filled with an insulating fill material 2, the semiconductor channel 1 of Figures 1 A- IB or the two wing portions la and lb of the semiconductor channel of Figure 3 have a wavy profile with a substantially uniform thickness, and the insulating fill material 2 is a quasi- cylindrical body having a variable thickness in a direction perpendicular to the major surface 100a of the substrate 100.
[0032] The wavy profile of the charge storage layer 9 results in a longer profile (in a direction substantially perpendicular to the major surface 100a) of the first and second curved charge storage segments 9a, 9b along the control gates 3a, 3b than a comparable flat segment of the charge storage layer. This longer, curved charge storage segments 9a, 9b provide a longer diffusion path for trapped electrons, and therefore reduces leakage to adjacent cells. The wavy profile of the charge storage layer 9 also enhances the electric field for the programmed cell (along charge storage segments 9a, 9b), and reduces the electric field in the spacing region adjacent the interlevel insulating layers (along charge storage segment 9c). As a result, interference between cells is reduced.
[0033] Figures 5A-5I illustrate a method of making a NAND string according to a first embodiment of the invention.
[0034] Referring to Figure 5A, an optional etch stop layer 202a is formed over the major surface 100a of the substrate 100. The etch stop layer 202a may be, for example, a polysilicon layer. In some embodiments, the etch stop layer 202a comprises a conductive or heavily doped semiconductor (e.g., n or p-type doped with a concentration of at least 1018 cm3) material, and the etch stop layer 202a forms the electrode 102a. In other embodiments, the etch stop layer 202a comprises a sacrificial material, at least a portion of which is removed to provide a space to form an electrode 102a. In some embodiments, the etch stop layer 202a is an insulating or semiconductor material and remains in the completed device 150. In yet other embodiments, etch stop layer 202a is omitted.
[0035] As shown in Figure 5B, a stack 120 of alternating first layers 19 (19a, 19b, etc.) and second layers 122 (122a, 122b, etc.) are formed over the etch stop layer 202a or over the major surface 100a of substrate 100 if the etch stop layer 202a is omitted. First layers 19 and second layers 122 may be deposited over the substrate by any suitable deposition method, such as sputtering, CVD, MBE, etc. First layers 19 may comprise an insulating material, for example a silicon oxide, in one embodiment, second layers 122 may comprise a conductive or semiconductive material, and the second layers 122 form the plurality of control gate electrodes 3. In another embodiment, second layers 122 are sacrificial layers, and may comprise a sacrificial material, such as intrinsic polysilicon or an insulating material (e.g., silicon nitride, silicon oxide, etc.). In these embodiments, the second layers 122 are removed, and a plurality of control gate electrodes is formed in their place by a replacement process.
[0036] The deposition of first layers 19 and second layers 122 is followed by etching the stack 120 to form at least one opening 84 in the stack 120, as shown in Figure 5c. An array of openings 84 may be formed in locations where vertical channels or channel portions of NAND strings will be subsequently formed. The etching process forms a first curved profile 84c in the first layers 19, and a second curved profile 84a, 84b in the second layers 122. As shown in Figure 5C, the first curved profile 84c is different from the second curved profile 84a, 84b. In some embodiments, the first curved profile 84c is convex in the direction of the opening 84 (i.e., curved sides of first layers 19 protrude into the opening 84), and the second curved profile 84a, 84b is concave in the direction of the opening 84 (i.e., curved sides of second layers 122 in the opening 84 curve inward into second layers 122).
[0037] In some embodiments, the etching of the stack comprises a dry etching process which results in the first curved profile 84c and the second curved profile 84a, 84b. For example, the dry etching process may be performed at any combination of parameters (e.g., pressure, temperature, chemical etchant, etc.) that results in the curved profile of the opening 84. In one embodiment, the etching of the stack comprises a first anisotropic etching process followed by a second selective etching process. For example, the first dry etching process may be a reactive ion etch, and the second selective etching process is a selective isotropic wet or dry etch which selectively recesses the second layers 122 compared to the first layers 19 to form the first curved profile 84c and the second curved profile 84a, 84b. In another embodiment, the etching of the stack is performed in a single step.
[0038J A blocking dielectric 7 (also known as an inter-poly dielectric, IPD) is then formed in the opening 84 such that the blocking dielectric coats the sides of the opening 84, resulting in a structure as shown in Figure 5D. The blocking dielectric 7 may comprise a silicon oxide layer deposited by conformal atomic layer deposition (ALD) or chemical vapor deposition (CVD). Other high-k dielectric materials, such as hafnium oxide or aluminum oxide, or multi-layer dielectrics (e.g., ONO) may be used instead or in addition to silicon oxide. Optionally, an insulating capping layer (e.g., silicon nitride) may be deposited into the openings before the blocking dielectric 7 and may comprise a back portion of a multi-layer blocking dielectric. The blocking dielectric 7 follows the curvature of the opening 84 to form a first curved blocking segment 7c on the first layers 19, and second curved blocking segments 7a, 7b on the second layers 122. In some embodiments, the blocking dielectric 7 has a substantially uniform thickness, and the first curved blocking segment 7c is convex in the direction of the opening 84, and the second curved blocking segments 7a, 7b are concave in the direction of the opening 84.
[0039] A charge storage layer 9 is formed in the openings 84 over the blocking dielectric material 7, resulting in the structure shown in Figure 5E. As explained above, in some embodiments, the charge storage layer 9 may comprise a charge storage dielectric material (e.g., silicon nitride). Alternatively, the charge storage layer 9 may comprise a conductive or semiconductor floating gate material (e.g., a metal, metal alloy such as TiN, metal silicide, or heavily doped polysilicon floating gate material). Any desired methods may be used to form the charge storage layer 9, such as ALD or CVD. The charge storage layer 9 follows the curvature of the blocking dielectric 7 to form a first curved charge storage segment 9c over the first layers 19, and second curved charge storage segments 9a, 9b over the second layers 122. In some embodiments, the charge storage layer 9 has a substantially uniform thickness, and the first curved charge storage segment 9c is convex in the direction of the opening 84, and the second curved charge storage segments 9a, 9b are concave in the direction of the opening 84. In other words, the first charge storage segment 9c is concave in the direction of the first layers 19, and the second charge storage segments 9a, 9b are convex in the direction of the second layers 122.
[0040] The tunnel dielectric 1 1 is deposited in the opening 84, over the charge storage layer 9, as shown in Figure 5F. This may be accomplished, for example by depositing the tunnel dielectric material 1 1 with a chemical vapor deposition (CVD) processor an atomic layer deposition (ALD) process. The tunnel dielectric 1 1 follows the curvature of the charge storage layer 9 to form a first curved tunnel segment 1 lc over the first layers 19, and second curved tunnel segments 1 1a, l ib over the second layers 122. In some embodiments, the tunnel dielectric 1 1 has a substantially uniform thickness, and the first curved tunnel segment 1 lc is convex in the direction of the opening 84, and the second curved tunnel segments 11a, 1 lb are concave in the direction of the opening 84. In various embodiments, the charge storage layer 9 and the tunnel dielectric 1 1 have a wavy profile along substantially the length of the opening 84.
[0041] As illustrated in Figure 5G, the channel 1 may be formed by depositing the semiconductor channel 1 , which comprises a semiconductor material, such as a lightly doped or intrinsic polysilicon, in the opening 84. As discussed above, the entire opening 84 may be filled to form the device illustrated in Figures 2A, 2B, and 4. In various embodiments, the semiconductor channel 1 has a circular cross section when viewed from above, and the semiconductor channel 1 completely fills the opening 84 with a semiconductor channel material. Alternatively, the semiconductor channel 1 may first be deposited in the opening 84 followed by deposition of an insulating fill 2 to form the device illustrated in Figures 1 A, I B, and 3. In various embodiments, the semiconductor channel 1 has a circular cross section when viewed from above, and the semiconductor channel material is formed over the side wall of the opening 84 but not in a central part of the opening 84 such that the semiconductor channel material does not completely fill the opening 84. An insulating fill 2 is formed in the central part of the opening 84 to completely fill the opening 84. If desired, the channel 1 may be U-shaped, as illustrated in Figures 3 and 4.
[0042] The semiconductor channel 1 follows the curvature of the tunnel dielectric 1 1 to form a first curved channel segment lc over the first layers 19, and second curved channel segments la, lb over the second layers 122. In some embodiments, the semiconductor channel 1 has a substantially uniform thickness, and the first curved channel segment lc is convex in the direction of the opening 84, and the second curved channel segments la, lb are concave in the direction of the opening 84.
[0043] As shown in Figure 5H, the insulating fill 2 is deposited to fill the opening in the semiconductor channel 1. The insulating fill 2 follows the curvature of the semiconductor channel 1 to form a quasi -cylindrical body having a variable thickness in a direction perpendicular to the major surface 100a of the substrate 100.
[0044] Figure 51 shows the completed NAND string 150 including the plurality of control gate electrodes 3 and source and drain electrodes 102a, 102b formed in electrical contact with respective end portions of the semiconductor channel 1. In various embodiments, a first electrode 102b is formed in electrical contact with an upper end of the semiconductor channel 1 , and a second electrode 102a is formed in electrical contact with a lower end of the semiconductor channel 1. In one embodiment, the plurality of control gate electrodes 3 are formed by etching the stack 120 to form a backside opening 184 (e.g., a slit trench or source electrode opening) in the stack such that the etch stop layer 202a is exposed. The etch stop layer 202a and the second layers 122 are removed from the stack 120 through backside opening 184 to form a plurality of recesses between the first layers 19, and the plurality of electrically conductive (e.g., metal, such as tungsten and/or metal nitride, such as TiN) control gates 3 and the source electrode 102a are formed in the plurality of recesses through the backside opening 184. In various embodiments, each of the plurality of control gates 3 has a profile complementary to the charge storage layer 9. In other embodiments, the source electrode 102a is in electrical contact with the lower end of the semiconductor channel 1 in the backside opening 184, and the drain electrode 102b is in electrical contact with the upper end of the semiconductor channel 1.
[0045] Although the foregoing refers to particular preferred embodiments, it will be understood that the invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.

Claims

WHAT IS CLAIMED IS:
1. A monolithic three dimensional NAND string, comprising:
a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of a substrate;
a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprises at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level;
an interlevel insulating layer located between the first control gate electrode and the second control gate electrode;
a blocking dielectric layer located in contact with the plurality of control gate electrodes and the interlevel insulating layer;
a charge storage layer located at least partially in contact with the blocking dielectric layer, and wherein the charge storage layer comprises at least a first charge storage segment located in the first device level, a second charge storage segment located in the second device level, and a third charge storage segment located adjacent to the interlevel insulating layer between the first device level and the second device level; and
a tunnel dielectric located between the charge storage layer and the semiconductor channel;
wherein the charge storage layer has a curved profile along at least one of the first charge storage segment and the third charge storage segment.
2. The monolithic three dimensional NAND string of claim 1 , wherein the charge storage layer has a first curved profile along the first charge storage segment and a second curved profile along the third charge storage segment, wherein the second curved profile is different from the first curved profile.
3. The monolithic three dimensional NAND string of claim 2, wherein the first curved profile is convex in the direction of the first control gate electrode and the second curved profile is concave in the direction of the interlevel insulating layer.
4. The monolithic three dimensional NAND string of claim 1, wherein the charge storage layer is continuous.
5. The monolithic three dimensional NAND string of claim 2, wherein the charge storage layer has a substantially uniform thickness.
6. The monolithic three dimensional NAND string of claim 1 , wherein the blocking dielectric layer has a complementary curved profile along at least one segment in contact with the charge storage layer.
7. The monolithic three dimensional NAND string of claim 6, wherein the blocking dielectric layer has a substantially uniform thickness.
8. The monolithic three dimensional NAND string of claim 6, wherein each control gate electrode of the plurality of control gate electrodes contacting the blocking dielectric layer has a complementary curved profile.
9. The monolithic three dimensional NAND string of claim 1 , wherein the tunnel dielectric has a complementary curved profile along at least one segment in contact with the charge storage layer.
10. The monolithic three dimensional NAND string of claim 9, wherein the tunnel dielectric has a substantially uniform thickness.
11. The monolithic three dimensional NAND string of claim 9, wherein the semiconductor channel has a complementary curved profile along at least one segment in contact with the tunnel dielectric.
12. The monolithic three dimensional NAND string of claim 11, further comprising an insulating core fill layer contacting the semiconductor channel.
13. The monolithic three dimensional NAND string of claim 12, wherein:
the semiconductor channel is a hollow quasi-cylindrical body having walls with a substantially uniform thickness, and
the insulating core fill layer is located inside the hollow quasi-cylindrical body and has a variable thickness in a direction perpendicular to the major surface of the substrate.
14. The monolithic three dimensional NAND string of claim 1 , wherein the charge storage layer has a wavy profile.
15. The monolithic three dimensional NAND string of claim 14, wherein blocking dielectric, the tunnel dielectric, and the semiconductor channel each have a complementary wavy profile to the charge storage layer.
16. The monolithic three dimensional NAND string of claim 1 , wherein:
the charge storage layer comprises silicon nitride;
the tunnel dielectric comprises silicon oxide, silicon oxynitride or a combination of silicon oxide and silicon nitride; and
the blocking dielectric layer comprises silicon oxide.
17. The monolithic three dimensional NAND string of claim 1 ,
wherein the semiconductor channel has a pillar shape and extends substantially perpendicular to the major surface of the substrate; and
further comprising one of a source or drain electrode which contacts the pillar-shaped semiconductor channel from above, and another one of a source or drain electrode which contacts the pillar-shaped semiconductor channel from below.
18. The monolithic three dimensional NAND string of claim 1 ,
wherein the semiconductor channel has U-shaped pipe shape,
wherein two wing portions of the U-shaped pipe shape semiconductor channel extend substantially perpendicular to the major surface of the substrate and a connecting portion of the U-shaped pipe shape semiconductor channel which connects the two wing portions extends substantially parallel to the major surface of the substrate; and
further comprising:
one of a source or drain electrode contacts the first wing portion of the semiconductor channel from above; and
another one of a source or drain electrode which contacts the second wing portion of the semiconductor channel from above.
19. The monolithic three dimensional NAND string of claim 1 ,
wherein the semiconductor channel has J-shaped pipe shape,
wherein a wing portion of the J-shaped pipe shape semiconductor channel extends substantially perpendicular to the major surface of the substrate and a connecting portion of the J-shaped pipe shape semiconductor channel which connects to the wing portion extends substantially parallel to the major surface of the substrate; and
further comprising:
one of a source or drain electrode contacts the first wing portion of the semiconductor channel from above; and
another one of a source or drain electrode which contacts the connecting portion of the semiconductor channel from above.
20. A monolithic three dimensional NAND memory device, comprising:
a silicon substrate;
an array of monolithic three dimensional NAND strings having a plurality of device levels disposed above the silicon substrate; and
driver circuits associated with the array located above or in the silicon substrate; wherein each monolithic three dimensional NAND string comprises:
a semiconductor channel, at least one end portion of the semiconductor channel extending substantially perpendicular to a major surface of the substrate; a plurality of control gate electrodes extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprises at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level located over the major surface of the substrate and below the first device level;
an interlevel insulating layer located between the first control gate electrode and the second control gate electrode;
a blocking dielectric layer located in contact with the plurality of control gate electrodes and the interlevel insulating layer;
a charge storage layer located at least partially in contact with the blocking dielectric layer, and wherein the charge storage layer comprises at least a first charge storage segment located in the first device level, a second charge storage segment located in the second device level, and a third charge storage segment located adjacent to the interlevel insulating layer between the first device level and the second device level; and
a tunnel dielectric located between the charge storage layer and the
semiconductor channel;
wherein the charge storage layer has a curved profile along at least one of the first charge storage segment and the third charge storage segment.
21. A method of making a monolithic three dimensional NAND string, comprising:
forming a stack of alternating first layers and second layers, wherein the first layers comprise an insulating material;
etching the stack to form at least one opening in the stack to form a first curved profile in the first layers in the at least one opening and to form a second curved profile in the second layers in the at least one opening, wherein the second curved profile is different from the first curved profile;
forming a charge storage layer in the at least one opening;
forming a tunnel dielectric over the charge storage layer in the at least one opening; and
forming a semiconductor channel over the tunnel dielectric in the at least one opening.
22. The method of claim 21 , wherein:
the semiconductor channel has a circular cross section when viewed from above; and the step of forming the semiconductor channel in the at least one opening forms a semiconductor channel material over the side wall of the at least one opening but not in a central part of the at least one opening such that the semiconductor channel material does not completely fill the at least one opening and an insulating fill material is formed in the central part of the at least one opening to completely fill the at least one opening.
23. The method of claim 21, wherein:
the semiconductor channel has a circular cross section when viewed from above; and the step of forming the semiconductor channel in the at least one opening completely fills the at least one opening with a semiconductor channel material.
24. The method of claim 21 , further comprising forming a first electrode in electrical contact with an upper end of the semiconductor channel and forming a second electrode in electrical contact with a lower end of the semiconductor channel.
25. The method of claim 21 , further comprising forming a blocking dielectric layer in the at least one opening.
26. The method of claim 21 , wherein the charge storage layer and the tunnel dielectric have a wavy profile along substantially the length of the at least one opening.
27. The method of claim 26, wherein the semiconductor channel has a wavy profile along substantially the length of the at least one opening.
28. The method of claim 21, wherein the charge storage layer is substantially uniform in thickness.
29. The method of claim 21 , wherein the etching of the stack comprises a dry etching process having at least one of a pressure and a chemical etchant content which result in the first curved profile and the second curved profile.
30. The method of claim 21 , wherein the etching of the stack comprises a first dry etching process followed by a second selective etching process.
31. The method of claim 30, wherein the first dry etching process is a reactive ion etch, and the second selective etching process is a selective isotropic wet etch which selectively recesses the second layers compared to the first layers to form the first curved profile and second curved profile.
32. The method of claim 21 , wherein the second layers comprise a sacrificial material.
33. The method of claim 21 , wherein:
the first layers comprise silicon oxide;
the second layers comprise silicon nitride; and
the charge storage layer comprises silicon nitride.
34. The method of claim 21, further comprising forming an etch stop layer such that the stack of alternating layers is formed over the etch stop layer.
35. The method of claim 34, further comprising:
etching the stack to form at least one first source electrode opening in the stack to expose the etch stop layer;
removing the second layers from the stack to form a plurality of recesses between the first layers in the stack; and
forming a plurality of control gate electrodes in the plurality of recesses through the first source electrode opening.
36. The method of claim 35, wherein each of the plurality of control gate electrodes has a profile complementary to the charge storage layer.
37. The method of claim 35, further comprising: forming a source electrode in electrical contact with a lower end of the semiconductor channel in the at least one first source electrode opening; and
forming a drain electrode in electrical contact with an upper end of the semiconductor channel.
38. The method of claim 21 , wherein the first curved profile is convex in the direction of the at least one opening and the second curved profile is concave in the direction of the at least one opening.
39. The method of claim 21, further comprising:
forming a insulating core fill layer over the semiconductor channel;
wherein the semiconductor channel is a hollow quasi-cylindrical body having walls with a substantially uniform thickness; and
wherein the insulating core fill layer is located inside the hollow quasi-cylindrical body and has a variable thickness in a direction perpendicular to the major surface of the substrate.
EP15727191.7A 2014-06-05 2015-05-20 Three dimensional nand device having a wavy charge storage layer Pending EP3152783A1 (en)

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